1. Field of the Invention
This invention relates to novel catalysts which contain Group VIIIA metals and which have been given severe thermal or hydrothermal treatments. The methods to make the catalysts as well as their methods of use are disclosed.
2. Description of the Previously Published Art
The zeolites ZSM-5 and ZSM-11, first described in U.S. Pat. No. 3,702,886 and U.S. Pat. No. 3,709,979, respectively, have been extensively investigated during recent years. These zeolites have more recently been given the designation MFI and MEL zeolites, respectively, in "Chemical Nomenclature, and Formulation of Compositions of Synthetic and Natural Zeolites" IUPAC yellow booklet, 1978. Together, the materials make up the family of the "pentasil" zeolites as discussed in Jacobs, P. A., and Martens, J. A. "Synthesis of High-Silica Aluminosilicate Zeolites" Studies in Surface Science and Catalysis, Vol. 33, Elsevier, New York, NY, 1987, Chapter IV.
There exist numerous patents describing the use of the MFI and MEL zeolites in hydrocarbon cracking reactions in conjunction with other zeolites as described in U.S. Pat. Nos. 3,702,886; 3,894,931; 3,894,933; and 3,894,934. More recently, there has developed an additive technology using especially MFI zeolites for enhancing the octane rating of gasoline. Illustrations of this technology can be found in U.S. Pat. Nos. 4,368,114; 4,309,279; 4,309,280; 4,289,606; and 3,758,403. These patents describe the addition of an octane enhancing additive such as MFI into a FCC process in order to boost the resulting gasoline's rating. The additive MFI cracks the low octane gasoline components such as paraffins to gas, thus removing them from the gasoline mixture. None of these patents recognize the unique ability of nickel to enhance the activity and selectivity of MFI or MEL zeolites in cracking reactions.
There is also technology for the upgrading of naphthas and FCC effluent as described in U.S. Pat. Nos. 3,770,614; 3,894,931; 4,784,745; and 4,806,230. In U.S. Pat. No. 4,806,230, a zinc or gallium containing MFI zeolite is used to upgrade hydrocarbon naphtha; U.S. Pat. No. 4,784,745 and U.S. Pat. No. 3,894,931 describe the improvement in the octane number or volatility of effluent from an FCC unit using MFI and MEL zeolites; and U.S. Pat. No. 3,770,614 describes the use of MFI to enhance the yield of aromatic hydrocarbons from low boiling reformate. None of these patents mention the use of nickel to enhance the activity or selectivity of the crystalline MFI or MEL zeolites.
Nickel containing MFI zeolite has been developed for use in the hydrodewaxing of lubricating oil stock as revealed in U.S. Pat. Nos. 4,642,176; 4,560,649; and 4,229,282. The use of Ni-MFI in the production of middle distillate from light olefins is described in U.S. Pat. No. 4,517,396. The use of Ni-MFI in gas oil hydrocracking, giving gasoline fractions of increased octane number is the object of U.S. Pat. No. 4,816,538. U.S. Pat. No. 3,755,145 claims the use of MFI zeolite in hydrocracking processes also. There has developed technology for the use of Ni-MFI zeolite for the synthesis of aromatic hydrocarbons using acidic forms of MFI zeolite as patented in S. U. 1,416,482; Japanese Patent Publication (unexamined) No. 156,889/1988; U. S. Pat. No. 3,827,867; and U.S. Pat. No. 4,766,265. There has also evolved technology for the production of aromatic hydrocarbons using non-acidic MFI zeolite as described in U. S. Pat. No. 4,652,360 and 4,347,394. These patents for base-exchanged zeolites are not relevant to the present invention, which is only concerned with the activity and selectivity of MFI and MEL zeolites in their acidic forms. The oligomerization of olefin containing feedstocks, particularly ethylene, using Ni-MFI can be found patented in U.S. Pat. Nos. 4,740,645, 4,608,450 and 4,551,438. Finally, the use of Ni-MFI zeolites for the conversion of synthesis gas to hydrocarbons is the subject of U.S. Pat. No. 4,543,347, and for shape selective reactions is described in U.S. Pat. No. 4,377,503. None of the above patented technology, however, recognizes the advantages of severe hydrothermal treatment of Ni-MFI and Ni-MEL zeolites in the particular reactions relevant to each patent.
U.S. Pat. No. 4,717,782, assigned to Mobil Oil, discloses using a nickel containing ZSM-5 catalyst to oligomerize ethene in the presence of a reducing component such as hydrogen and a co-feed of water. The water is present in an amount to maintain the nickel component of the oligomerization catalyst in an oxidized state. Once the water co-feed is terminated, the Ni-ZSM-5 catalyst looses its selectivity advantages. The gas stream containing ethene in the presence of hydrogen is converted into liquid hydrocarbons. The presence of water under the mild reaction conditions described does not convert the Ni-MFI permanently into the unique zeolite as described herein.
Mild steaming of shape-selective zeolites has been disclosed by Chester et al. in U.S. Pat. Nos. 4,429,176 and 4,522,929 as enhancing both the alpha activity and stability of such catalysts in acid-catalyzed reactions such as xylene isomerization. U.S. Pat. No. 4,559,314 to Shihabi teaches that very highly siliceous shape-selective zeolites, which are inactive, can be activated by steaming the alumina bound zeolite. These patents, however, do not recognize the combined effect of hydrothermal treatment with added nickel on the catalytic activity and selectivity in hydrocarbon reactions.
3. Objects of the Invention
It is an object of this invention to prepare a novel catalyst with improved activity and selectivity characteristics after severe thermal or hydrothermal pretreatments in catalytic reactions.
It is a further object of this invention to prepare a catalyst with improved activity and selectivity after severe thermal and hydrothermal treatments for processes involving the cracking of paraffinic hydrocarbons, such as may occur in refinery effluents.
It is a further object of this invention to prepare a catalyst with improved selectivity to aromatic hydrocarbons in processes involving the cracking of paraffinic hydrocarbons.
It is a further object of this invention to prepare a catalyst which produces improved research and motor octane number product in processes involving the cracking of paraffinic hydrocarbons.
It is a further object of this invention to prepare a catalyst which produces greater gasoline yield in processes involving the cracking of paraffinic hydrocarbons.
It is a further object of this invention to prepare a catalyst that shifts to higher average molecular weight the hydrocarbon products produced in processes involving the cracking of paraffinic hydrocarbons.
These and further objects will become apparent as the invention proceeds.